Hydrated lead borate products



United States Patent 3,126,351 HYDRATED LEAD BORATE PRODUCTS Laurence R. Blair, Gillette, and Karlie 1L. Jauuarajs,

Somerville, N J assignors to Johus-Manville Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Dec. 31, 1%8, Ser. No. 734,080

12 Qlairns. (Cl. 252-478) This invention relates to an improved shielding material or medium for noxious radiation, especially neutrons, and more particularly to an effective neutron absorbent boron material or composition which is self-bonding and may be molded or shaped separately or in combination with other neutron or gamma ray shielding materials into handleable, mechanically self-supporting, structural shapes or bodies, or applied as cementitious or mortarlike materials.

Progress in the development and application of atomic reactors, cyciotrons and in related fields involving radioactive materials, the increased utilization thereof, with the inherently noxious radioactive emanations produced thereby has brought about an urgent need for improved and more adaptable shielding materials or mediums for the protection of personnel and adjacent equipment from such noxious radiation. While noxious radioactive emanations, e.g., gamma rays, neutrons or the like, and radioactive shielding materials or mediums have long been known, understood and utilized, conventional shields comprising bulky masses of dense materials such as lead, concrete, steel, etc., present numerous obvious and inherent disadvantages. These conventional types of materials, in general, are of necessity, heavy, massive and bulky, lacking adaptability in many applications and convenient fabrication and/or installation, and notwithstanding such inherent disadvantages, frequently are not efficient in attenuating or aborbing neutrons. Moreover, exposure of many typical shielding materials to radiation frequently induces radioactivity in the shielding material whereby the shield itself may disseminate noxious radiation, i.e., secondary radiation.

In many applications shields comprising massive and bulky high density structures are giving way to more efiicient and practical protective structures consisting of effective neutron energy reducing and absorbing compositions such as high. hydrogen and/or boron containing materials alone or in combination with high density gamma radiation absorbing materials. Boron, of course, is an almost unique clement insofar as slowing and capturing slow or thermal neutrons is concerned because of its ability to absorb large amounts of thermal neutrons while emitting only soft /2 m.e.v.) gamma rays and readily absorbed alpha particles. United States Letters Patent No. 2,796,529 and No. 2,727,996, for example, fully describe several radiation shielding mediums or constructions embodying metallic boron or boron compounds dispersed discontinuously and uniformly throughout a supporting matrix such as synthetic resin or malleable metal. Such boron containing shielding mediums have included boron in a number of forms, such, for example, as elemental boron, natural borate minerals suc has colernanite or borax, boric acid, boron organic compounds, synthetically produced boron carbide, boron alloys such as aluminum-boron carbide, aqueous solutions of boron salts and the like. These materials or their application in the prior art, however, almost without exception are subject to one or more material disadvantage. For example, among other reasons apparent to those skilled in the art, boron metal, boron carbide or the like are very expensive, many boron containing materials or compounds are not stable when subjected to elevated temperatures or exposed to moisture or oxidizing conditions and therefore require expensive or cumbersome waterproofing and weatherproofing, or the inexpensive and stable boron compounds are not generally available in mechanically self-retaining or self-supporting structural and/ or readily moldable forms and are therefore diflicult to set into place around reactors, conduits, etc., without the use of a hinder or supporting matrix. Typical bonding materials by themselves are not effective in shielding or absorbing radiation and their use may substantially reduce the boron content or density of a shielding medium and thereby necessitate the use of a heavier and/ or thicker shield to provide the high boron concentrations required. Moreover, radioactivity may be induced into some bonding materials whereby they become a secondary source of radiation.

A principal object of this invention is to provide an insoluble, heat resistant inorganic self-bonding borate compound which may be molded or shaped into strong and handleable but workable, mechanically self-supporting, shape retaining structural bodies or units of substantially any configuration desired, and a method of preparing the same.

A further object of this invention is to provide an effective and emcient shielding medium for noxious radioactive emanations comprising an insoluble, inorganic self-bonding neutron absorbing compound of relatively high borate content which may be shaped or molded into handleable, mechanically self-supporting, shape re taining structural bodies or units.

A further object of this invention is to provide a relatively low cost, water resistant, stable, self-bonding high capacity slow or thermal neutron absorbing borate shielding composition which may be provided as shape retaining mechanically self-supporting structural units or' bodies, or as a plastic, cohesive mass with cementitious or mortarlike properties or characteristics, which upon drying results in a mechanically self-supporting structural mass.

A further object of this invention is to provide a mechanically self-supporting structural borate shielding material or composition for slow or thermal neutrons which has a relatively low thermal conductivity, is stable at high temperatures and is an eflicient and effective thermal insulation as well as a shielding absorbent for noxious radioactive emanations.

A still further object of this invention is to provide selfbonding, plastic, cohesive cementitious or mortar-like boron compositions which have neutron absorbing. properties, are readily applicable, self-setting and low cost, and can be utilized to produce mechanically self-supporting, structural monolithic-like masses or mortar bonded joints which absorb neutrons and are water and heat resistant, stable, and efficient thermal insulators.

This invention will be more fully understood and further objects and advantages thereof will become apparent from a consideration of the following detailed description of the invention.

In general, the objects of this invention are obtained by a radiation shield, and thermal insulation, comprising a Patented Mar. 24, 1964 water insoluble gel precipitate or reaction product of an aqueous solution of borax with a soluble acid salt of lead. These soluble acid salts of lead may be prepared from or comprise an inorganic acid such as nitric, or an organic acid such as acetic, provided that the salts solubility is adequate, i.e., a solubility of at least approximately 1 part by weight of the salt per 3 parts by weight of water. The solubility of the reactants is material as pointed out hereinafter and very slightly soluble salts are not satisfactory. The relative amounts or ratios of borax and soluble lead salts in the aqueous solution should be such as to provide, on an oxide basis, approximately 1-2 mole of B for each mol of lead oxide. Formation or precipitation of the gel reaction product and the characteristics of said gel reaction product or precipitate are substantially enhanced by effecting the reaction at solution temperatures ranging from that approximating room temperatures (6070 F.) up to about 200 F. The resultant insoluble reaction product or precipitate is a voluminous gel with cohesive self-bonding properties, and the precipitate must be gelatinous in nature in that crystalline precipitates, lacking cohesiveness or self-adherence, cannot be shaped, molded or otherwise provided as self-bonded, mechanically self-supporting, handleable structural bodies or shapes. Dewatering or consolidation of the resulting slurry of gel precipitate is typically desirable or even necessary, depending, of course, upon the concentration(s) of the solution(s) containing the reactants, and, in turn, the water to solids ratio of the resulting gel precipitate slurry and the characteristics desired in the final product, e.g., whether or not the gel precipitate is to be shaped or molded into handleable structural units or poured like concrete and the desired density thereof. It should be understood, however, that dewatering or consolidation may be effected by substantially any conventional means such as compression molding, filtering or the like, and because of the large quantities of water typically present in the gel precipitate slurries notwithstanding the use of reactant solutions of maximum concentration, dewatering of the gel precipitate is usually necessary and preferred in the preparation of either shaped structural units or a plastic cohesive cement.

Formation of a gel precipitate and its characteristics, as indicated hereinbefore, are influenced by the solution temperatures. For example, effecting the formation of the gel precipitate at temperatures ranging between approximately 68 and 208 F. results in gel precipitate yields ranging between 80-100% and a temperature of approximately 86 F. results in about a maximum or approximately 100% yield. Thus, although reaction temperatures are significant and an optimum yield or recovery certainly desirable, other factors or considerations, in particular obtaining a sufliciently high solids to water ratio of the resulting gel precipitate slurry to permit practical and economical dewatering and forming of shaped products or a workable cement, are equally significant. In other words, the low solubility of some reactants, particularly borax, at low temperatures such as those which influence maximum precipitate yield, e.g., room temperature up to approximately 100 F., generally produce reactive solutions which result in gel precipitate slurries having water to solids ratios too high for efiicient, economical dewatering and/ or molding. Thus, to a point, the higher the temperature of the aqueous solvent the greater the amount of borax and/or soluble reactants soluble therein, and the greater the concentration of solids to water ratio which materially facilitates dewatering. Accordingly, it is to be understood that the preferred or optimum conditions for efficient and economical practice of this invention are the result of a compromise between apparently contrary factors, i.e., the optimum temperature conditions for maximum precipitation and the optimum temperature conditions for the maximum dissolution or maximum solids to water ratio of the solution. Moreover, it has also been found that the gel precipitates formed at higher temperatures generally have better fil- 4 tering properties. Typically preferred aqueous temperatures for dissolving reactants such as borax therefore comprise those ranging between about to 190 F., preferably approximately 140 F. for the dissolution of borax, although it is to be understood that a suitable gel may be precipitated at temperatures ranging anywhere from about 60 to 210 F. High dissolution temperatures and subsequent cooling of the saturated solution prior to precipitation may be utilized, of course, as a means of attempting to achieve maximum efficiency, but in accordance with generally known principles, excessive cooling must be avoided and care taken to avoid premature precipitation of the reactive solute from the resulting supersaturated solution prior to the desired reaction. Borax being only slightly or moderately soluble, requires elevated temperatures, usually at least approximately F. and preferably about F. to achieve a borax solution of suilicient concentration to result in an economical solids to water ratio, e.g., about 100 lbs. of borax to 50 gals. of water. Readily soluble lead salts may be added to cold water because of their solubility, and a cold solution thereof may be added to the borax solution without materially impeding the reaction because the resulting lead borate gel precipitate removes borax from solution at a rapid rate preventing saturation of the borax solution.

Solutions of boric acid and sodium hydroxide or sodium carbonate, or other equivalents for borax may be substituted for the latter but such sources of boron typically complicate the procedure and add additional raw materials which generally increases cost. Soluble lead salts of mineral acids such as nitric, or, organic acids such as acetic and the like, if sufficiently soluble, have been found to produce insoluble gel precipitates which are filterable and self-bonding. Further, such salts are typically readily soluble in aqueous solution, generally low cost and easy to handle.

Dewatering of the aqueous slurry of borate gel precipitate and consolidation of the same way be effected by any suitable conventional means. For example, substantially any filtration means or method such as simple filtration, preferably expedited by a pressure differential such as a vacuum or high pressure head provided by a pump, press filtration comprising hydraulic or mechanical means of applying pressure, or the like may be utilized with varying degrees of economy and efficiency in extracting the excess water from the gel precipitate. Preferably a press comprising a bed having a filtering body such as a firmly supported wire screen or perforated plate and a hydraulically actuated press platen is employed, whereby strong compression may be applied to the slurry containing the borate gel precipitate to result in an efficient high degree of dewatering and compressing or molding of said gel, particularly wherein a shaped, handleable object is desired. Of course, the press bed and platen may be such as to impart substantially any shape or configuration to the object being dewatered and/ or molded. If the gel precipitate is to be utilized as a cohesive cement, dewatering should be just suificient to provide a plastic, workable, or fiowable cohesive mass of the consistency of typical ement or mortar.

Because of their intended use, that of a shielding means or medium for noxious radiation, the hydrated lead borate products of this invention should be prepared at substantially the highest density practical. For example, densities of at least approximately 65 p.c.f. are desired to provide maximum resistance to radiation. Density, of course, is dependent upon dewatering and/or consolidating efliciency and press capacity and, in general, the greater the density the more effective the shield. High densities, however, reduce the thermal insulating characteristics of the properties and where a low thermal conductivity is desired or necessary the density may be lowered.

An essential and meritorious characteristic of this hydrated lead borate gel precipitate or reaction product is its cohesive or self-bonding property which permits the utilization of the borate material as either a mechanically self-supporting structural shape or as a plastic cementitious or mortar-like self-adhering cohesive mass without the addition of an extraneous or non-neutron absorbing binder, or a retaining and supporting matrix or means which diminishes the unit volume neutron absorbing efficiency of the product. Moreover, this cohesive, self-bonding property of the hydrated borate gel materially facilitates the preparation of the borate radiation shields in that upon adequate dewatering and/ or shaping of the precipitate gel slurry the material whether shaped or applied as a cementitious mass need only be dried. Drying of the dewatered and/ or shaped product, if a shaped object is desired, may be effected simply by exposure to temperatures ranging from ambient up to about 1000" F., elevated temperatures in the range between 250 F. and 500 F. being preferred in that they are economical and hasten the drying. Thus, manufacture of the borate shielding products does not require the typical but expensive and involved curing or reacting of binders or other components to provide a handleable, mechanically self-supporting structural object or shape.

Preferably, the hydrated borate gel precipitate or reaction products, whether molded or otherwise shaped into handleable, self-supporting structural shapes or simply utilized as a cohesive self-bonding cement or mortar, are reinforced with reinforcing fiber. Suitable reinforcing fiber desirably comprises heat resistant inorganic fiber such as asbestos or an amphibole, glass, mineral wool or the like, but organic fiber such as cellulose, animal, vegetable, synthetic, etc., may sufiice for low temperature applications. Fiber may be incorporated in the gel products in substantially any amount, for example, up to approximately 30% by Weight of the final product; however, excessive quantities beyond appropriate reinforcing needs, though not necessarily detrimental, obviously reduce the amount of neutron absorbing borate per unit volume and therefore may not be desirable. Approximately -10% by weight of the final product has been found generally to impart adequate strength or reinforcement for most requirements but it should be noted that the fiber content depends of course upon the intended ultimate use or strength requirements desired in the ultimate product.

It has been further found that filtration time for the borate gel precipitate can be decreased and the density of the hydrated borate gel product increased Without a decrease of the boron density by the addition of an insoluble high born containing filler such as the mineral colemanite or Gerstley borate. Gerstley borate is a tradename for a mixture of the natural minerals colemanite (Ca B O and ulexite (NaCaB O -8H O). To decrease the water content of the fillers and further increase their boron content and increase their heat stability, the boron containing filler can be calcined or fritted. Suitable calcination temperatures for colemanite comprise 1100 to 1400 F. and 800 to 1100 F. for Gerstley borate. Fritting temperatures for either of these materials are in excess of 1900 F. Further, substantially any radiation attenuating material may comprise a suitable filler, for example, particulate metallic lead, iron or the like heavy elements and compounds of such materials, materials or compounds comprising a source of water, etc. The filler(s), if any, and/ or the amount of the same depends, of course, upon the characteristics desired or the requirements of the particular installation or application. Fillers, however, may normally be included in any amount up to approximately 70% by weight of the total.

Hydrogen is also a good absorbent and barrier for neutrons, and water, being a ready and economical source of hydrogen therefore may be a desirable component of a borate gel product. For example, a susbtantial water content is advantageous where shielding fast neutrons is also desirable or necessary. Other applications, however, particularly wherever there is a possibility that liquid sodium metal might contact the borate shield, require a substantially Water free product and this may be achieved simply by firing the dried borate products at temperatures up to about 1000 F. Temperatures in the region of 850 to 950 F. normally effect adequate water removal for safe use of the product with sodium metal containing installations.

The hydrated borate compositions comprising this improved radiation shield etfectively resist all typical deleterious elements or conditions such as radiation, high temperatures and the like normally present in or about reactors, cyclotrons, radioactive materials, etc. For example, shaped hydrated borate products prepared in accordance with this invention resist soaking temperatures up to 1500 F. and repeated exposure of one side to temperatures of 1000" F. Without any indication of cracking or spalling. Moreover, these products Withstand neutron flux equivalent to 2.4 10 nvt and gamma flux equivalent to 2X10 m.e.v./cm. /sec. without affecting their resistance to crushing or suffering any damage or deterioration.

The following examples illustrate typical hydrated lead borate gel compositions, products thereof and methods of manufacturing the same. It is to be understood that the specific compositions of the borate gels are exemplary and are not to be construed to limit the invention to the proportions of reactants or the reaction conditions specified in the examples.

Example I A lead borate gel product was produced by preparing a borax solution comprising 190.5 grams of borax dissolved in 1000 ml. of hot (158 F.) water and a solution of a soluble acid salt of lead comprising 331.23 grams of lead nitrate (Pb (N09 dissolved in 600 ml. of hot (158 F.) water, and combining the resulting solutions of borax and lead nitrate. Chrysotile asbestos fiber in amount of 30 grams was added to and dispersed throughout the gel product precipitated from the combined solutions. The slurry of fiber-lead borate precipitate was placed in a 6"x6" press with a perforated platen and shaped into a block under a pressure of 15,000 lbs. The pressed block was handleable, mechanically self-supporting and, upon drying at 248 F. for 24 hours, was a rigid, structural but workable mass exhibiting considerable strength.

Example 11 A like lead borate gel product was similarly produced from a soluble organic acid salt of lead by dissolving 19.0 grams of lead acetate (Pb(C H O -3H O) in 40 ml. of water and 19.1 grams of borax in ml. of hot F.) water and combining these solutions at a temperature of 149 F. The resulting lead borate gel precipitate, upon filtration, dewatering and drying at 248 F. for 24 hours, was structurally strong, rigid and handleable exhibiting physical properties comparable to those of the product of Example I.

For reasons clearly apparent from the foregoing disclosure the terms soluble or solubility as used throughout this specification and the appended claims are intended to denote or define the capability of at least approximately 1 part by Weight of a solute to mix (dissolve) with 3 parts by weight of an aqueous liquid (solvent) to form a homogeneous mixture (solution). In other words for practical, efficient and economical practice of this invention, the acid salts of lead should have a solubility of at least approximately 35 grams per 100 ml. of water and the scope of this invention as defined by the claims should be so construed.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

What we claim is:

1. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, water insoluble hydrated borate gel, which comprises forming a water insoluble hydrated borate gel precipitate by combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B for each mol of lead oxide and at a temperature within the range of approximately 60-200 F.

2. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, Water insoluble hydrated borate gel, which comprises forming a water insoluble hydrated borate gel precipitate by combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B 0 for each mol of lead oxide and at a temperature within the range of approximately 120-l90 F.

3. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, water insoluble hydrated borate gel reinforced with fiber, which comprises forming a water insoluble hydrated borate gel precipitate by combining, in an aqueous solution, borax and Water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B 0 for each mol of lead oxide and at a temperature within the range of approximately 60-200 F., and providing throughout said gel precipitate reinforcing fiber in amount up to approximately by weight of the total material.

4. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, water insoluble hydrated borate gel containing particulate filler of radiation attenuating materials, which comprises forming a water insoluble hydrated borate gel precipitate by combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B 0 for each mol of lead oxide and at a temperature within the range of approximately 60200 F., and providing throughout said gel precipitate particulate filler comprising radiation attenuating materials in amount up to approximately 70% by weight of the total material.

5. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, water insoluble hydrated borate gel reinforced with fiber and containing particulate filler of radiation attenuating materials, which comprises forming a water insoluble hy drated borate gel precipitate by combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B 0 for each mol of lead oxide and at a temperature within the range of approximately 60-200 F., and providing throughout said gel precipitate reinforcing fiber in amount up to approximately 30% by weight of the material and particulate filler comprising radiation attenuating materials in amount up to approximately 70% by weight of the material.

6. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, water insoluble hydrated borate gel reinforced with fiber and containing particulate filler of radiation attenuating materials, which comprises forming a water insoluble hydrated borate gel precipitate by combining, in aqueous solution, borax and Water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on

an oxide basis, of about 1-2 mols of B 0 for each mol of lead oxide and at a temperature within the range of approximately -190" F., providing throughout said gel precipitate reinforcing fiber in amount up to approximately 30% by weight of the material and particulate filler comprising radiation attenuating materials in amount up to approximately 70% by weight of the material, and compressing the fiber reinforced, filled, gel precipitate to de-water and shape the same.

7. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, Water insoluble hydrated borate gel reinforced with fiber and containing particulate filler of radiation attenuating materials, which comprises forming a water insoluble hydrated borate gel precipitate by combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B 0 for each mol of lead oxide and at a temperature of approximately F., providing throughout the said gel precipitate inorganic reinforcing fiber in amount of approximately 5-10% by weight of the material and particulate filler comprising radiation attenuating materials in amount up to approximately 70% by weight of the material, and compressing the fiber reinforced, filled, gel precipitate to de-water, shape and consolidate the same to a density of at least about 65 lbs. per cu. ft.

8. The method of preparing a structural borate neutron shielding material consisting essentially of self-bonding, water insoluble hydrated borate gel reinforced with fiber, which comprises forming a Water insoluble hydrated borate gel precipitate by combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B 0 for each mol of lead oxide and at a temperature of approximately 140 F., providing throughout the said gel precipitate inorganic reinforcing fiber in amount of approximately 5-10% by Weight of the total material, and compressing the fiber reinforced gel precipitate to de-water, shape and consolidate the same to a density of at least about 65 lbs. per cu. ft.

9. A structural borate neutron shielding material consisting essentially of the self-bonding, water insoluble borate gel precipitate reaction product of combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about l-2 mols of B 0 for each mol of divalent metal oxide and at a temperature within the range of approximately 60-200 F.

10. A structural borate neutron shielding material consisting essentially of the fiber reinforced, self-bonding, water insoluble borate gel precipitate reaction product of combining in aqueous solution, borax and water insoluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about 1-2 mols of B 0 for each mol of divalent metal oxide and at a temperature within the range of approximately 60-200 F., with reinforcing fiber in amount up to approximately 30% by weight of the total material.

11. A structural borate neutron shielding material consisting essentially of the filled, self-bonding, water insoluble hydrated borate gel precipitate reaction product of combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about l-2 mols of B 0 for each mol of divalent metal oxide and at a temperature within the range of approximately 60-200" F., with particulate filler of radiation attenuating materials in amount up to approximately 70% by weight of the total material.

12. A structural borate neutron shielding material consisting essentially of the fiber reinforced, filled, self-bonding, water insoluble hydrated borate gel precipitate reaction product of combining, in aqueous solution, borax and water soluble lead salts of an acid selected from the group consisting of nitric and acetic, and mixtures thereof, in an approximate ratio, on an oxide basis, of about l-2 mols of B 0 for each mol of divalent metal oxide and at a temperature within the range of approximately 60-200" F., with reinforcing fiber in amount up to approximately 30% by weight of the material and particulate filler of 10 radiation attenuating materials in amount up to approximately 70% by weight of the material.

References Cited in the file of this patent UNITED STATES PATENTS 2,405,366 Myhren et al. Aug. 6, 1946 10 2,607,658 Govett et al Aug. 19, 1952 2,716,705 Zinn Aug. 30, 1955 2,717,240 Fronmuller Sept. 6, 1955 2,726,339 Borst Dec. 6, 1955 2,727,996 Rockwell Dec. 20, 1955 2,747,105 Fitzgerald et al May 22, 1956 2,796,411 Zirkle June 18, 1957 2,836,500 Weidman May 27, 1958 OTHER REFERENCES Mellor: A Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. V, 1924, p. 106, pub. Longmans, Green & Co., New York.

Rose: The Condensed Chemical Dictionary, 5th ed., 1956, p. 115, pub. Reinhold Pub. Corp., New York. 

1. THE METHOD OF PREPARING A STRUCTURAL BORATE NEUTRON SHIELDING MATERIAL CONSISTING ESSENTIALLY OF SELF-BONDING, WATER INSOLUBLE HYDRATED BORATE GEL, WHICH COMPRISES FORMING A WATER INSOLUBLE HYDRATED BORATE GEL PRECIPITATE BY COMBINING, IN AQUEOUS SOLUTION, BORAX AND WATER SOLUBLE LEAD SALTS OF AN ACID SELECTED FROM THE GROUP CONSISTING OF NITRIC AND ACETIC, AND MIXTURES THEREOF, IN AN APPROXIMATE RATIO, ON AN OXIDE BASIS, OF ABOUT 1-2 MOLS OF B2O3 FOR EAHC MOL OF LEAD OXIDE AND AT A TEMPERATURE WITHIN THE RANGE OF APPROXIMATELY 60-200*F.
 9. A STRUCTURAL BORATE NEUTRON SHIELDING MATERIAL CONSISTING ESSENTIALLY OF THE SELF-BONDING WATER INSOLUBLE BORATE GEL PRECIPITATE REACTION PRODUCT OF COMBINING, IN AQUEOUS SOLUTION, BORAX AND WATER SOLUBLE LEAD SLATS OF AN ACID SELECTED FROM THE GROUP CONSISTING OF NITRIC AND ACETICK AND MIXTURES THEREOF, IN AN APPROXIMATE RATIO, ON AN OXIDE BASIS, OF ABOUT 1-2 MOLS OF B2O3 FOR EACH MOL OF DIVALENT METAL OXIDE AND AT A TEMPERATURE WITHIN THE RANGE OF APPROXIMATELY 60-200*F. 